This invention concerns a value document such as a bank note, and a method for checking the presence of the same.
Safeguarding the authenticity of value documents by means of luminescent substances has been known for some time. Preferably, host lattices doped with rare earth metals are used, with the absorption and emission regions being variable within a broad range through suitable coordination of rare earth metal and host lattice. It is also per se known to employ magnetic and electrically conductive materials for safeguarding authenticity. Magnetism, electrical conductivity and luminescence emission are detectable by machine using commercially available measuring instruments, while luminescence with emission in the visible region in sufficient intensity is also detectable visually.
Practically as old as safeguarding the authenticity of value documents is the problem of the value documents' authentication features being forged. Anti-forgery security can be increased for example by employing not only one feature substance, but a plurality of feature substances in combination, for example a luminescent substance and a magnetic substance, or a luminescent substance and a substance influencing the luminescence properties. DE 10 2005 047 609 A1 describes feature substances for safeguarding the authenticity of value documents which contain a luminescent substance and at least one further substance that is preferably magnetic or electrically conductive. The luminescent substance is present in particulate form and is surrounded by a shell formed of nanoparticles. The properties of the feature substance result from the interaction of the luminescence emission properties of the luminescent substance and the properties of the nanoparticles.
Starting out from this prior art, the present invention is based on the object of providing a value document that is improved in terms of anti-forgery security, and a method for checking the presence of the same.